1. Field of the Invention
The present invention relates to a flame retardant resin composition comprising a radically polymerizable resin modified with a phosphorus-containing compound.
2. Prior Art
In the production of laminates, a continuous production method is practically used, in which all the steps from the immersion of a substrate in a resin varnish to the shaping are continuously carried out.
FIG. 1 shows one example of such a continuous method for the production of laminates.
Firstly, each elongate substrate 1, which is wound around a respective roll is continuously unwound and passed through a resin-immersing bath 2 to impregnate the substrate 1 with a resin varnish. Then, a plurality of the substrates 1, which have been impregnated with the resin varnish, are continuously passed through rolls 3, 3. In this step, elongate metal foils 4 such as copper foils are also passed through the rolls 3, 3 while laminating them on the both sides of the laminated substrates. Thereafter, the composite of the substrates 1 and the metal foils 4 is passed through a heat curing furnace 5 to cure the resin varnish impregnated in the substrates so that the substrates 1 and the metal foils 4 are integrally laminated. The laminate is then pulled out from the furnace 5, and cut to a desired size with a cutting machine 6. Thus, laminates A are obtained.
In the case of a composite laminate such as CEM-3, glass woven fabrics 1a and glass non-woven fabrics 1b are used as substrates, and a laminate is produced by laminating the glass woven fabrics 1a impregnated with a resin varnish as outer layers, and the glass non-woven fabrics 1b impregnated with a resin varnish as inner layers.
When laminates are produced by the above-described continuous method, a resin varnish impregnated in substrates is heated and cured in a heat curing furnace without pressurization. Thus, a resin varnish comprising a radically polymerizable resin is generally used, which contains no solvent as a volatile component, or generates no water or other volatile components by the curing reaction.
Furthermore, to make a laminate flame retardant, it is necessary to incorporate a halogen atom such as a bromine atom or a chlorine atom in the backbones of a radically polymerizable resin.
However, when laminates are produced using such a radically polymerizable resin containing a halogen atom such as a bromine atom or a chlorine atom, the halogen atom is liberated from the resin on burning of the laminate to generate toxic gasses such as hydrogen bromide or hydrogen chloride gas, dioxin, etc., which may have harmful influences on human beings or the environment.
One object of the present invention is to provide a resin composition which is made flame retardant without the use of a halogen atom such as a bromine atom or a chlorine atom.
Accordingly, the present invention provides a flame retardant resin composition comprising a radically polymerizable resin which is modified with a phosphorus-containing compound of the formula (1): 
wherein R is a hydrogen atom or a group of the formula: xe2x80x94(CH2)nxe2x80x94R1 in which R1 is a group derived from a compound having at least two phenolic hydroxyl groups or epoxy groups, and n is an integer of 0 to 3.